Audible signal apparatus



Dec. 20, 1966 w s 3,292,571

AUDI'BLE SIGNAL APPARATUS Original Filed Aug. '7, 1959 2 SheetsSheet 1 I NVENTOR. B/AL 65M? M77525 Dec. 20, 1966 B. G. WATTERS AUDIBLE S IGNAL APPARATUS Original Filed Aug. 7, 1959 P vaer/mz/ 1 0F HORN SPILDB 2 Sheets-Sheet 2 INVENTOR.

I izwhflui United States Patent 3,292,571 AUDIBLE SIGNAL APPARATUS Bill Gene Watters, Nahant, Mass., assignor to Wallace & Tiernau Iuc., Belleville, N.J., a corporation of Delaware Original application Aug. 7, 1959, Ser. No. 832,284, now Patent No. 3,138,795, dated June 23, 1964. Divided and this application May 8, 1964, Ser. No. 366,059

Claims. (Cl. 116137) This patent application is a division of United States patent application Serial No. 832,284 filed August 7, 1959, entitled, Electronic Audible Horn, now US. Patent No. 3,138,795.

This invention relates to audible signal apparatus and particularly to apparatus suitable for use as a fog horn in a location which is exposed to the weather and where the apparatus may be unattended for long periods of time.

There has recently arisen a demand for fog horns which will operate without attention for a period of months and which will meet high standards of reliability.

Since the horns are sometimes mounted in locations Where they are subject to spray and even to occasional immersion under high wave conditions, it is required that the horn structure be capable of withstanding such waves and spray without substantial adverse effect on the operation of the horn. It is desired to run these horns for months without any maintenance work, and it is customary to operate each one under the control of a motor-driven time switch, so that it operates day and night in clear weather or in fog. For example, a typical horn may run on a cycle of two seconds of sound followed by eighteen seconds of silence.

Each horn must have its own source of energy, commonly storage batteries. In order to insure that the battery life is as long as possible, the components of the horn must be made highly efficient.

Such a horn is commonly operated by a driver or transducer energized by an oscillator. In order to secure high effective efficiency, the horn must be constructed so that the sound spreads to a maximum distance in a horizontal plane, without substantial waste of energy in directing the sound vertically.

An object of the present invention is to provide an improved audible signal apparatus including a horn and a driver or transducer for vibrating a column of air in the horn.

A further object is to provide an apparatus of the type described in which the components operate at a fixed frequency and without maintenance for long periods of time.

A further object is to provide apparatus of the type described which may be mounted in a location exposed to marine atmosphere, spray and waves, without being adversely affected.

Another object of this invention is to provide a compact horn structure for operation at a predetermined operating frequency in which the acoustic impedance of the horn is non-reactive.

The foregoing and other objects of the invention are attained in the apparatus described herein. This apparatus includes a double horn located in a vertically extending, generally cylindrical housing. The horn has two vertically spaced mouths opening at the periphery of the housing and having equal vertical dimensions. The mouths open horizontally and extend around the entire periphery of the housing. The horn includes a single throat, a first horn portion, at least part of which is tapered, extending between the throat and a fork, and second and third tapered horn portions extending respectively between the fork and the upper and lower mouths. The fork is located midway between the mouths and substantially along the axis of the housing. The second and third tapered por- 3 ,292,5 71 Patented Dec. 20, 1966 tions of the horn extend respectively upwardly and downwardly from the fork and curve so that they are tangent with the horizontal at the respective mouths. The throat is located within the casing at one side thereof and between the second tapered portion and the upper mouth. The first portion of the horn extends horizontally from the fork and curves generally upwardly to the throat, crossing the upper end portion of the horn. A constant diameter tube has one end opening into the throat and extends therefrom to the upper end portion of the housing. The driver or transducer for vibrating the air in the horn is mounted Within the upper end portion of the housing, at one end of a resonating chamber whose opposite end opens into the upper end of the constant diameter tube.

The horn portion connected to the upper mouth curves downwardly and inwardly from that mouth, so that any water or spray entering the upper mouth flows downwardly into the horn. The horn portion connected to the lower mouth curves inwardly and upwardly from that mouth and communicates with the horn portion leading to the upper mouth at the fork in the center of the housing. By virtue of this arrangement any water or spray entering either mouth flows downwardly through the horn portions and out through the lower mouth. Since the portion of the horn between the throat and the fork curves upwardly from the fork, any water or spray entering that portion of the horn drains down into the fork and thence out through the lower mouth.

For maximum overall efficiency, it is desirable to have the acoustic impedance of the horn non-reactive, i.e., resistive at the operating frequency. A non-resonant horn would require an overall diameter somewhat larger than a wave length. For the selected frequency of 400 cycles per second, the wave length is approximately one meter. In order to utilize a somewhat smaller structure While retaining substantially non-reactive characteristics for the horn, the sound reflecting condition at the horn mouth due to its small dimensions is balanced by providing a resonating chamber between the throat and the driver.

The driver or transducer for vibrating the air in the horn, and the means from which the driver or transducer receives its energy, may be of conventional construction. However, the preferred construction for the driver or transducer and the associated energizing apparatus is in accordance with the teachings of the United States patent application Serial No. 832,284, filed August 7, 1959, for an Electronic Audible Horn, of which the present application is a division. The present invention will be described in relation to this preferred construction for the driver. A more complete description of this preferred driver is to be found in the parent application.

Other objects and advantages of the invention will become apparent from a consideration of the following specification and claims, taken together with the accompanying drawings.

In the drawings:

FIG. 1 is a view, partly in elevation and partly in section, showing a fog horn embodying the invention;

FIG. 2 is a sectional view, taken on the line II-II of FIG. 1, looking in the direction of the arrows;

FIG. 3 is a sectional View taken on the line IIIIII of FIG. 2, looking in the direction of the arrows;

FIG. 4 is a view, partly in section, on the line IV-IV of FIG. 2, and partly in elevation; and

FIG. 5 is a graphical illustration, taken on a vertical plane through the fog horn, showing the pattern of distribution of sound from the fog horn.

The horn There is shown in FIG. 1 a fog horn including a generally cylindrical housing 1 having its axis vertical and adapted for mounting on a horizontal plane support. Within the housing 1 there is located a double exponential horn, generally indicated by the reference numeral 2, which tapers from a throat 2a to a large end which includes an upper mouth 2b and a lower mouth 2c vertically spaced from the upper mouth. The horn may be described as a vertical linear array of two in-phase sources of sound. The mouths extend around the entire periphery of the housing and each month is sectionaliZed by a plurality of radial vanes 21:. A constant diameter portion 20! leads from the throat 2a to a tapered portion 2d, which extends to a fork 2e. From the fork 2e, a second tapered portion 21'' extends upwardly to the mouth 2b, and a third tapered portion 2g extends downwardly to the mouth 2c. The tapered portion 2 curves downwardly and inwardly from the mouth 2b to the fork 2e. The tapered portion 2g similarly curves inwardly and upwardly from the mouth 20 to the fork 2c. The tapered portions 2] and 2g together form a drain passage for any water or moisture which may enter through either of the mouths 2b and 2c. The drain passage allows all such water to flow down and out through the lower mouth 20. The tapered portion 2d curves downwardly from the portion 2d and extends substantially horizontally into the fork 2e. Any moisture which may get into the portions 2d and 2d is drained downwardly through them and into the fork 2e where it may readily pass through the tapered portion 2g to the mouth 2c.

A constant diameter tube 3 has a gooseneck portion extending from the throat 2a and a vertical portion at the other end of a gooseneck. The upper end of the tube 3 abuts against one side of an orifice 50a (FIG. 3) formed in an orifice plate 50 mounted by means of screws 50b on the under side of a driver cover 51. The tube 3 has a sliding fit in the plate 50. In the cover 51 is formed a cylindrical aperture which receives a central projection on the plate 50 and also receives a piston 6. The piston 6, cover 51 and plate 50 define a cylindrical resonating chamber indicated by the reference numeral 5.

The lower end of tube 3 (FIG. 1) abuts against the upper end of the tapered throat 2a, as best seen in FIG. 1. The tube 3 and throat 2a are held together by a rubber hose coupling 4, held in place by coil spring clips 4a.

The'fog horn illustrated is designed to operate at 400 cycles. For maximum overall efliciency of the driver and horn combination, the mechanical load or impedance imposed upon the driver by the horn means, which includes the horn 2, the tube 3, and the coupling chamber 5, should be non-reactive. Further, the magnitude of the mechanical impedance should be such that the over-all efliciency of the fog horn is as high as possible, consistent with the maximum allowable deflection of the driver. The mechanical impedance can be adjusted so as to be non-reactive and to have the desired magnitude by adjusting the length of the constant diameter tube 3, the length of the larger resonating chamber 5, and the diameter of the throat 2a and tube 3. These elements constitute the parameters of an impedance matching network and may be adjusted to give the aforementioned maximum efiiciency consistent with the allowable driver deflection.

All the elements of the horn from the throat 2a back to the piston may be regarded as an acoustic coupling device whose dimensions and characteristics may be designed to suit the needs of each particular embodiment of the invention.

The diameter of the horn portion 2d which crosses the upper tapered portion 2 of the horn is so small as compared to the wave length of the sound that it makes no substantial difference in the distribution pattern.

The various lengths involved must be selected to place the surface of the piston at a peak of the standing wave which is set up between the piston and the mouth of the horn. If the piston is so placed, the mechanical load on it is resistive (non-reactive). If the piston is placed at any point other than a peak or a null of the standing wave, the load on the piston is then reactive rather than resistive. A peak is selected for the piston position rather than a null since the peak position requires less piston movement to produce a given sound intensity level at a given distance outside the horn mouth. A null point of the Wave always occurs at the horn mouth. Other nulls appear at every half wave length back from the mouth. It follows that a peak occurs at a quarter wave back from each null. The various lengths may be adjusted as necessary to place the piston at a peak.

On the top of the housing 1 is mounted a cylindrical casing 52, covered by a dome 53. The casing 52 and dome 53 enclose a driver, generally indicated in FIG. 1 by the reference numeral 54, an oscillator, generally indicated by the reference numeral 55, and a timer 56. Power is supplied to the unit from an external battery through a conduit 57.

The horn 2', casing 52, and dome 53 are preferably molded of glass reinforced plastic material, which is highly resistant to corrosion by marine atmosphere.

Driver 54 is supported on studs 58, threaded on a fixed platform 52a molded in the casing 52. A chamber 59 is formed by walls 52b, molded in the casing 52, and a cover 60 which sealingly encloses the chamber against entrance of moisture. The timer 56 and the oscillator 55 are located in the sealed chamber 59.

The timer 56 is a continuously running motor-driven switch, preferably adjustable to select any desired program over a range, for example, from two seconds of sound in six minutes to continuous sound.

The frequency of the audible signal changes to some extent with atmospheric conditions because of inherent loading effects, i.e., changes in the mechanical load on the horn. Since the horn is balanced to be substantially non-reactive, however, its characteristics are not substantially modified by such load variations. Consequently, the mechanical resonant frequency of the driver is the determining factor in the frequency of the sound. It has been found that atmospheric conditions may change the frequency of the note by not more than plus or minus 4%.

The driver The mechanism which supports the piston 6 and vi: brates it as 400 cycles is hereinafter referred to as the driver, and is illustrated in FIGS. 2, 3 and 4. The piston 6 is mounted by means of four spacer studs 7a (FIG. 3) on the bottom of a spool 13 which supports a driver coil 14. A pair of horizontally extending yokes 8 are mounted above piston 6 and against the bottom of the spool 13. The yokes 8 have central apertures to receive a beam 9 (FIGS. 2 and 4), preferably in the form of -a cylindrical tube, which projects a substantial distance in both directions beyond the yokes 8. The beam 9 is supported at its ends by means of spring members 10.

The spool 13 and coil 14 are mounted in an air gap 15 formed in a magnetic circuit including a central permanent magnet pole piece 16 and magnetic yoke members 17, 18 and 19 which complete the circuit between the ends of the pole piece 16. The air gap 15 is between one end of the pole piece 16 and a concentric aperture formed in the yoke member 19.

The driver assembly, including the beam 9 and its spring supports 10, and the parts mounted at the middle of the beam 9, including principally the piston 6, the spool 13 and coil 14, are designed so that their natural frequency of vibration is the frequency of the note desired from the horn. In the embodiment illustrated, this frequency is 400 cycles per second. The spring supports 10 serve as frictionless pivots for the ends of beam 9, and its center vibrates vertically (as shown in FIG. 3). The peak-to-peak amplitude of vibration, in various physical embodiments of the invention, has ranged from 0.020 to 0.080 inch. This vibration is accomplished by supplying the coil 14 with square Wave electrical energy at 400 cycles frequency.

An O-ring seal 20 (see FIG. 4) is provided between the piston 6 and the cylindrical wall of the chamber 5. The wall .of the chamber 5 is provided with a groove for receiving the O-ring. The axial dimension of the groove, as it appears in the drawing, is made slightly greater than the diameter of the O-ring. The difference between the groove width and the O-ring diameter should be slightly more than the amplitude of vibration of the beam 9. By virtue of the spacing of the O-ring, it rolls back and forth during vibration of the piston, so that there is no sliding friction either between the piston and the O-ring or between the O-ring and the wall. This rolling seal allows the piston to vibrate freely at the natural frequency of the vibrating assembly, without substantial damping due to frictional load.

A non-magnetic plate 22 encircles the pole piece 16 near the air gap 15 and has a flange 22a projecting toward the yoke member 19. An O-ring 23 seals the gap between the flange 22;: and the yoke member 19. The plate 22a and O-ring 23 serve to prevent passage of moisture into the vibrating assembly. The space around the vibrating assembly is connected through a passage 51a (FIG. 3) in the cover 51 to the interior of a container 24 which may be filled with a suitable desiccant, e.g., silica gel, for the purpose of maintaining the atmosphere at the vibrating assembly in a completely dry condition.

The driver may be energized by an oscillator connect ed to coil 14. The oscillator may be of conventional construction, but a preferred construction is in accordance with the teachings of the parent patent application Serial No. 832,284.

FIG. 5

This figure illustrates graphically the distribution of sound waves on a vertical plane taken through the fog horn 1. It may be seen that the sound is distributed horizontally substantially equally in all directions, and that the maximum sound intensity is in the horizontal direction. There are two minor lobes to the distribution pattern vertically above and below the fog horn. With the exception of these two minor lobes, the energy of the horn is expended where it will be most useful, i.e., in a horizontal direction. The two mouths of the double horn have been spaced apart vertically, so as to maximize the transmission of sound in the horizontal direction. The resulting directivity pattern is shown in FIG. 5. In this plot the sound pressure level measured at a radius of 25 feet is shown as a function of the polar angle. The sound pressure level is essentially independent of the azimuthal angle. tween the mouths of the horn in FIG. 1 was chosen to give a minimum of sound radiation at a polar angle of about 40.

The effectiveness of a directive sound source such as the double fog horn is measured by the directivity index:

sound intensity at a distance r in the desired (horizontal) direction The theory for the sound radiation from two, small, in-phase sound sources shows that the D1. reaches a maximum of about 4 db when the spacing between the sources is about 0.72 times the wavelength of sound. The center-to-center spacing of the mouths of the horn of FIG. 1 was chosen to be slightly les than 0.72 wave length; the smaller spacing giving a D.I. only slightly lower than 4 db and a somewhat broader main lobe (i.e., one having a greater vertical dimension) than would be the case for a spacing of 0.72 wavelength. This broader main lobe is desirable in a device such as a fog horn, mounted close to the surface of the water and intended to produce signals audible on the bridges of ships which may have a considerably greater elevation than the fog horn.

While I have shown and described a preferred embodiment of my invention, other modifications will read- The vertical spacing be- 6 ily occur to those skilled in the art, and I therefore intend my invention to be limited only by the appended claims.

I claim:

1. Audible signal apparatus operable at a predetermined acoustical frequency comprising a generally cylindrical housing having its cylinder axis vertical, a double horn within the housing and having two vertically spaced upper and lower mouths with equal vertical dimensions, said mouths opening horizontally and extending around the periphery of the housing, said horn including a single throat, a fork, and a first tapered horn portion between the throat and the fork, and second and third tapered horn portions between the fork and the respective upper and lower mouths, said fork being located midway between the mouths and substantially along the axis of the housing, said second and third portions extending respectively upwardly and downwardly from the fork and curving to horizontal directions at the respective mouths, said first portion extending horizontally from the [fork and curving to the throat, an acoustic coupling device extending from the throat, a driver for said horn located within said housing and including a movable wall in a chamber constituting a portion of said acoustic coupling device, said acoustic coupling device being dimensioned to provide an acoustic reactance between said throat and said driver which balances the reactance of the horn months so that the mechanical load on the movable wall is effectively non-reactive at the acoustical frequency of operation.

2. Audible signal apparatus comprising a generally cylindrical housing having its cylinder axis vertical, a double horn within the housing and having two vertically spaced upper and lower mouths with equal vertical dimensions, said mouths opening horizontally and extending around the periphery of the housing, said horn including a single throat, a fork, and a first tapered horn portion between the throat and the fork, and second and third tapered horn portions extending between the fork and the respective upper and lower mouths, said fork being located midway between the mouths and substantially along the axis of the housing, said second and third portions extending respectively upwardly and downwardly from the fork and curving to horizontal directions at the respective months, said first portion extending horizontally from the fork and curving through one of said second and third portions of the horn to an end portion of the housing, and means within the housing for Vibrating the air in said throat to produce a uniformly horizontally distributed sound.

3. Audible signal apparatus for use in a location exposed to precipitation and spray, comprising a generally cylindrical housing having its cylinder axis vertical, a double born within the housing and having two vertically spaced upper and lower mouths with equal vertical dimensions, said mouths opening horizontally and extending arotmd the periphery of the housing, said horn including a single throat, a fork, and a first tapered horn portion extending between the throat and the fork, and second and third tapered horn portions extending between the fork and the respective upper and lower months, said horn portion being curved, said fork being located midway between the mouths and substantially along the axis of the housing, said second and third portions extending respectively upwardly and downwardly from the fork and curving to be tangent to the horizontal at the respective mouths, said second and third portions providing a drain for water entering either mouth to discharge through the lower mouth, said first portion extending horizontally from the fork and curving toward a generally upward direction at the throat, said first portion providing a drain for any water therein through the first horn portion and thence through the third horn portion and out the lower mouth, and means within the housing for vibrating the air in the horn to produce sound waves at the mouths of the horn.

4. A fixed frequency audible signal apparatus comprising a horn having a throat and a mouth smaller than the minimum size required for a non-reactive acoustic impedance at said fixed frequency, a driver including a wall vibratable at said fixed frequency, and an acoustic coupling device between the wall and the throat and dimensioned to provide an acoustic reactance between the throat and driver which balances the reactance of the horn mouth so that the mechanical load on the wall is effectively non-reactive at said fixed frequency.

5. Audible signal apparatus comprising a generally cylindrical housing, a double horn within the housing and having two axially spaced mouths with equal axial dimensions, said mouths each opening radially and extending around the periphery of the housing, said horn including a single throat, a fork, and a first tapered horn portion between the throat and the fork, and second and third tapered horn portions extending between the fork and the respective mouths, said fork being located midway between the mouths and substantially along the axis of the housing, said second and third portions extending in opposite directions axially away from the fork and curving to radial directions at the respective months, said first portion extending radially from the fork and curving through one of said second and third portions of the horn to an end portion of the housing, and means within the end portion of the housing for vibrating the air in said throat to produce a uniformly distributed sound generally in the region of a plane perpendicular to the axis of said housing.

6. A sound generator operable to emit sound of a predetermined frequency comprising a cylindrical housing, a double horn having two mouths axially spaced in said housing and opening through the walls thereof, said mouth openings extending around the entire periphery of said housing and being sectionalized by a plurality of radial vanes so that each mouth has sections for radiating sound in all radial directions perpendicular to the axis of said housing, means for providing acoustic input energy comprising a wall vibratable at said predetermined frequency, an acoustic structure connected between said input means and said horn mouths, said acoustic structure defining a chamber, said vibratable wall forming one wall' of said chamber, said acoustic structure including tubular connections from said chamber to said months, said tubular connections including smoothly tapered portions providing progressively larger cross-sectional areas terminating in said horn mouths, said tapered portions inculding a fork positioned midway between said mouths for dividing the output from said vibratable wall between said mouths.

7. Signal apparatus in accordance with, claim 6 in which the axial spacing between said mouths is about 0.72 times the wavelength of the sound to be emitted.

8. A sound generator operable to emit sound of a predetermined frequency comprising a cylindrical housing, a double horn having two months axially spaced in said housing and opening through the walls thereof, said mouth openings extending around the entire periphery of said housing and being sectionalized by a plurality of radial vanes so that each month has sections for radiating sound in all radial directions perpendicular to the axis of said housing, the maximum dimensions of each of said mouths being less than a wave length of the sound at said frequency, means for providing acoustic input energy comprising a wall vibratable at said predetermined frequency, an acoustic structure connected between said input means and said horn mouths, said acoustic structure including tubular connections from said chamber to said mouths, said tubular connections including a fork at an axial position within said housing midway between said mouths, said acoustic structure being dimensioned to place said movable wall at a peak of the acoustical standing wave therein having a null at the horn mouths.

9. A sound generator operable to emit sound of a predetermined frequency comprising a housing, a horn having at least one mouth opening through the wall of said housing, the maximum dimension of said mouth being less than a wave length of said sound, means for pr0viding acoustic input energy comprising a wall vibratable at said predetermined frequency, an acoustic structure connected between said input means and said horn mouth, said acoustical structure being dimensioned to place said movable wall at an acoustical distance from said horn mouth as measured through said structure which is equal to a whole multiple of one-quarter of a wavelength of the sound at said frequency.

10. A sound generator in accordance with claim 9 in which said acoustical distance through said structure is equal to an odd whole multiple of one-quarter of a wave length of said sound to place said movable wall at a peak of the acoustical standing wave within said structure.

References Cited by the Examiner UNITED STATES PATENTS 1,752,526 4/1930 Hickley 18127 2,058,132 10/1936 Cirelli 181-27 2,206,427 7/ 1940 Preston 181-31 2,489,653 11/1949 Leslie 18131.1 3,138,795 6/1964 Wallace et al. 116-137 LOUIS J. CAPOZI, Primary Examiner. 

1. AUDIBLE SIGNAL APPARATUS OPERABLE AT A PREDETERMINED ACOUSTICAL FREQUENCY COMPRISING A GENERALLY CYLINDRICAL HOUSING HAVING ITS CYLINDER AXIS VERTICAL, A DOUBLE HORN WITHIN THE HOUSING AND HAVING TWO VERTICALLY SPACED UPPER AND LOWER MOUTHS WITH EQUAL VERTICAL DIMENSIONS, SAID MOUTHS OPENING HORIZONTALLY AND EXTENDING AROUND THE PERIPHERY OF THE HOUSING, SAID HORN INCLUDING A SINGLE TROAT, A FORK AND FIRST TAPERED HORN PORTION BETWEEN THE THROAT AND THE FORK, AND SECOND AND THIRD TAPERED HORN PORTIONS BETWEEN THE FORK AND THE RESPECTIVE UPPER AND LOWER MOUTHS, SAID FORK BEING LOCATED MIDWAY BETWEEN THE MOUTHS AND SUBSTANTIALLY ALONG THE AXIS OF THE HOUSING, SAID SECOND AND THIRD PORTIONS EXTENDING RESPECTIVELY UPWARDLY AND DOWNWARDLY FROM THE FORK AND CURVING TO HORIZONTAL DIRECTIONS AT THE RESPECTIVE MOUTHS, SAID FIRST PORTION EXTENDING HORIZONTALLY FROM THE FORK AND CURVING TO THE THROAT, AN ACOUSTIC COUPLING DEVICE EXTENDING FROM THE THROAT, A DRIVER FOR SAID HORN LOCATED WITHIN SAID HOUSING AND INCLUDING A MOVABLE WALL IN A CHAMBER CONSTITUTING A PORTION OF SAID ACOUSTIC COUPLING DEVICE, SAID ACOUSTIC COUPLING DEVICE BEING DIMENSIONED TO PROVIDE AN ACOUSTIC REASTANCE BETWEEN SAID THROAT AND SAID DRIVER WHICH BALANCES THE REACTANCE OF THE HORN MOUTHS SO THAT THE MECHANICAL LOAD ON THE MOVABLE WALL IS EFFECTIVELY NON-REACTIVE AT THE ACOUSTICAL FREQUENCY OF OPERATION. 